Escherichia coli 0157 cause severe enteritis and hemolytic uremic syndrome with their highest incidence in children. Infections caused by this pathogen may cause outbreaks in institutions with a high morbidity and mortality. In the United States, E. coli 0157 has been found to be the most common cause of visits to hospital clinics and hospitalization for dysentery. Control of enteric infections with E. coli 0157 is considered a high priority by the Centers for Disease Control and Prevention. The long-term objective of this project is to prevent enteric infections caused by E. coli 0157 and their complications by vaccination. The primary objective of this project is to evaluate three investigational 0157-rEPA conjugate vaccines in healthy adult volunteers (Phase 1 Study). The safety of the vaccines will be determined by the analysis of the reactions and results of liver function tests. The seroconversion rates, post-immunization levels, biologic activity and duration of vaccine- induced LPS antibodies will be evaluated to determine the immunogenicity of the vaccines. If these results are satisfactory, an efficacy study will be done to evaluate the vaccines in at-risk populations.